Clostridium difficile, often called C. difficile or C. diff, is a bacterium that can cause symptoms ranging from diarrhea to life-threatening inflammation of the colon. Clostridium difficile infection (CDI), also known as Clostridium difficile-associated diarrhea (CDAD), became a medically recognized infectious disease, initially as clindamycin colitis, over 3 decades ago. In the U.S. alone there are several hundred thousand cases per year, with a conservative estimated cost approaching $10,000 per case. CDAD/CDI is a significant health concern worldwide, resulting from the colonization and infection of the bowel by Clostridium difficile, a Gram-positive, spore-forming, obligate anaerobic bacterium. Clostridium difficile causes diarrhea and other intestinal disease when competing bacteria in the gut flora are wiped out by antibiotics. Even though much has been learned about CDAD/CDI, still many unsolved questions remain, particularly in the diagnostic field.
CDAD/CDI remains the most important infectious cause of diarrhea that develops from health care contact. While patient isolation and environmental disinfection appear to help in the control of CDAD/CDI, the effectiveness of infection control measures has been inconsistent. Outbreaks of particularly aggressive infection recently have appeared. One report involving a surgical unit found 5% of their patients with CDAD/CDI required surgical intervention, and overall there was an associated mortality rate of 3.5%. Since then, recognition of outbreaks from this hypervirulent Clostridium difficile strain (BI or NAP1), represented by a genotype overproducing toxins and harboring multiple resistance phenotypes, have been reported from Canada and the United States. Another alarming development has been the recognition that there are strains incapable of expressing an intact toxin A that can still cause disease and death. This observation complicates the current laboratory diagnosis since many of the common tests employed by clinical microbiology laboratories are immunoassays only detecting toxin A.
CDAD/CDI has also been recognized as the most commonly diagnosed reason for bacterial diarrhea in persons infected with HIV, further expanding the clinical impact of this infectious disease. CDAD/CDI appears to be growing in prevalence for many populations. With recent reports of hypervirulent disease from Canada and the United States, the diagnosis of this infection is critical as we are now faced with potentially more life-threatening as well as more antibiotic-resistant CDAD/CDI infections.
CDAD/CDI is a globally important, yet poorly diagnosed, healthcare-associated infectious disease. Importantly, the causative agent of this disease has become a crucial emerging pathogen with new virulent strains seen in the hospital, apparent emergence of community acquired disease, and recognition of CDAD/CDI as a key pathogen for HIV-infected persons. Understanding all these important biologic observations will be dependent on accurate diagnostic testing that is now largely lacking.
The diagnosis of CDAD/CDI in today's environment is based on clinical and laboratory findings because of current suboptimal laboratory diagnostic capabilities. A case definition for the usual presentation of CDAD/CDI includes: (i) diarrhea, typically defined as at least six watery stools over 36 hours, (or eight stools during 48 hours), (ii) a history of antimicrobial agent therapy within eight weeks of the onset of diarrhea, (iii) pseudomembranes seen at lower gastrointestinal endoscopy (this is required for the diagnosis of colitis), or a stool sample positive for the presence a toxin B (or toxins A and B), or a toxigenic isolate of Clostridium difficile (toxin B or toxins A and B) recovered from the stool, and (iv) no other reason for diarrhea.
Since 10 to 30% of hospitalized patients can be colonized with Clostridium difficile, and 20% of hospitalized patients experience some diarrhea, evaluating stools from patients without all the clear risk factors for CDAD/CDI using current technology testing only for the presence of Clostridium difficile or its toxins, with no objective measure of host response, leads to false positive clinical diagnostics. Thus, suboptimal detection of true disease combined with substantial reporting of false positive results indicates an urgent need for a better, fully objective diagnostic test. Current laboratory testing is limited to detection of the Clostridium difficile organism and/or its toxin product(s) and does not differentiate infected from simply colonized patients, thus leading to inaccurate diagnosis as well as antibiotic mis/overuse.
Accordingly, there is a need in the art for more specific and sensitive diagnostic methods for CDAD/CDI that will improve patient care by enabling specific, correct treatment at a very early time point, thus lowering the potential risk of severe disease and death as well as lower the overuse of antimicrobial agents. The following disclosure describes the specifics of such methods.